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POLICY AND PRACTICE REVIEWSpublished: 19 June 2019

doi: 10.3389/fmars.2019.00337

Edited by:Frank Edgar Muller-Karger,University of South Florida,

United States

Reviewed by:Scott Doney,

University of Virginia, United StatesPhilip Bresnahan,

University of California, San Diego,United States

*Correspondence:Bronte Tilbrook

bronte.tilbrook@csiro.au

Specialty section:This article was submitted to

Ocean Observation,a section of the journal

Frontiers in Marine Science

Received: 09 November 2018Accepted: 03 June 2019Published: 19 June 2019

Citation:Tilbrook B, Jewett EB,

DeGrandpre MD,Hernandez-Ayon JM, Feely RA,

Gledhill DK, Hansson L, Isensee K,Kurz ML, Newton JA, Siedlecki SA,

Chai F, Dupont S, Graco M, Calvo E,Greeley D, Kapsenberg L, Lebrec M,

Pelejero C, Schoo KL andTelszewski M (2019) An Enhanced

Ocean Acidification ObservingNetwork: From People to Technology

to Data Synthesis and InformationExchange. Front. Mar. Sci. 6:337.

doi: 10.3389/fmars.2019.00337

An Enhanced Ocean AcidificationObserving Network: From People toTechnology to Data Synthesis andInformation ExchangeBronte Tilbrook1,2* , Elizabeth B. Jewett3, Michael D. DeGrandpre4,Jose Martin Hernandez-Ayon5, Richard A. Feely6, Dwight K. Gledhill3, Lina Hansson7,Kirsten Isensee8, Meredith L. Kurz3, Janet A. Newton9, Samantha A. Siedlecki10,Fei Chai11,12, Sam Dupont13, Michelle Graco14, Eva Calvo15, Dana Greeley6,Lydia Kapsenberg15, Marine Lebrec7, Carles Pelejero15,16, Katherina L. Schoo8 andMaciej Telszewski17

1 Commonwealth Scientific and Industrial Research Organisation, Oceans and Atmosphere, Hobart, TAS, Australia,2 Antarctic Climate and Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, TAS, Australia, 3 OceanAcidification Program, National Oceanic and Atmospheric Administration, Silver Spring, MD, United States, 4 Departmentof Chemistry and Biochemistry, University of Montana, Missoula, MT, United States, 5 Instituto de InvestigacionesOceanológicas, Universidad Autónoma de Baja California, Ensenada, Mexico, 6 Pacific Marine Environmental Laboratory,National Oceanic and Atmospheric Administration, Seattle, WA, United States, 7 Ocean Acidification InternationalCoordination Centre, International Atomic Energy Agency Environment Laboratories, Monaco, Monaco, 8 IntergovernmentalOceanographic Commission of the United Nations Educational, Scientific and Cultural Organization, Paris, France, 9 AppliedPhysics Laboratory and College of the Environment, University of Washington, Seattle, WA, United States, 10 Departmentof Marine Sciences, University of Connecticut, Groton, CT, United States, 11 State Key Laboratory of Satellite OceanEnvironment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China, 12 School ofMarine Sciences, University of Maine, Orono, ME, United States, 13 Department of Biological and Environmental Sciences,University of Gothenburg, Kristineberg, Sweden, 14 Instituto del Mar del Perú, Lima, Peru, 15 Institut de Ciències del Mar,Consejo Superior de Investigaciones Científicas, Barcelona, Spain, 16 Institució Catalana de Recerca i Estudis Avançats,Barcelona, Spain, 17 Institute of Oceanology of the Polish Academy of Sciences, Sopot, Poland

A successful integrated ocean acidification (OA) observing network must include (1)scientists and technicians from a range of disciplines from physics to chemistry tobiology to technology development; (2) government, private, and intergovernmentalsupport; (3) regional cohorts working together on regionally specific issues; (4) publiclyaccessible data from the open ocean to coastal to estuarine systems; (5) closeintegration with other networks focusing on related measurements or issues includingthe social and economic consequences of OA; and (6) observation-based informationalproducts useful for decision making such as management of fisheries and aquaculture.The Global Ocean Acidification Observing Network (GOA-ON), a key player in thisvision, seeks to expand and enhance geographic extent and availability of coastal andopen ocean observing data to ultimately inform adaptive measures and policy action,especially in support of the United Nations 2030 Agenda for Sustainable Development.GOA-ON works to empower and support regional collaborative networks such as theLatin American Ocean Acidification Network, supports new scientists entering the fieldwith training, mentorship, and equipment, refines approaches for tracking biologicalimpacts, and stimulates development of lower-cost methodology and technologies

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allowing for wider participation of scientists. GOA-ON seeks to collaborate with andcomplement work done by other observing networks such as those focused on carbonflux into the ocean, tracking of carbon and oxygen in the ocean, observing biologicaldiversity, and determining short- and long-term variability in these and other oceanparameters through space and time.

Keywords: Global Ocean Acidification Observing Network, Sustainable Development Goal, ocean acidification,ecosystem stressors, capacity building

INTRODUCTION

The ocean has absorbed approximately 30% of anthropogeniccarbon dioxide (CO2) emissions since the industrial era began(Intergovernmental Panel on Climate Change (IPCC), 2013).Ocean acidification (OA), or the ongoing observed increase inmarine acidity, is a direct result of this uptake (Doney et al., 2009;Intergovernmental Panel on Climate Change (IPCC), 2013). Theaverage surface ocean pH has decreased by approximately 0.11units from a preindustrial mean value of 8.17, this representsan increase of about 28% in hydrogen ion concentration(Intergovernmental Panel on Climate Change (IPCC), 2013). Bythe end of this century, surface ocean pH is expected to decline byanother 0.1–0.4 units, and carbonate ion (CO3

2−) concentrationis expected to decline by as much as 50% over the same periodcompared to preindustrial conditions (Feely et al., 2004; Orr et al.,2005; Doney et al., 2009; Gattuso et al., 2015).

Ocean acidification has the potential to impact marineorganisms in a variety of ways, including effects from decreasedpH, elevated partial pressure of CO2 (pCO2), and decreasesin the calcium carbonate (CaCO3) saturation state. Changes inthe CaCO3 saturation state (Feely et al., 2004) make conditionscorrosive for many calcifying organisms such as many speciesof molluscs, corals, echinoderms, and calcifying plankton, withpotential dissolution of calcareous structures such as shells orskeletons (Eyre et al., 2018; Harvey et al., 2018). Changingcarbonate chemistry also impacts the process of calcificationin many species (Kroecker et al., 2013; Albright et al., 2016;Bednaršek et al., 2017). Less direct impacts can occur wheredeclines in calcification of key habitat forming organisms resultin ecosystem shifts and loss of the structural complexity andbiodiversity of coral reefs and other benthic communities(Fabricius et al., 2014; Sunday et al., 2016). Negative impactsof changing ocean carbonate chemistry have already beenobserved in calcifying organisms living in some regions of coastalupwelling where natural acidity is relatively high (Bednaršeket al., 2014, 2017). Research also suggests that changing oceanchemistry and reduced pH may affect the physiology, behavior,and population dynamics of many non-calcifying species (Doneyet al., 2009; Gattuso et al., 2015).

Over the past decade, the OA research community has grownrapidly, and the number of publications related to OA has grownexponentially (Figures 1, 2). In the context of this burgeoninggrowth, the ocean observing community recognized a need forglobal coordination at OceanObs’09 (Feely et al., 2010) andhas since made progress on collaborative efforts. The potentialimpacts to marine ecosystems have resulted in OA becoming

one of only ten targets for the United Nations (UN) SustainableDevelopment Goal (SDG) 14 on the conservation and sustainableuse of marine resources. The World Meteorological Organizationhas also included OA as a headline climate indicator, recognizingthe link to increasing atmospheric carbon dioxide concentrationsand the climate system. The challenges facing OA researchers,current and future coordinating activities, and a vision in lightof the upcoming United Nations Decade of Ocean Science forSustainable Development (2021–2030) for future OA observingare discussed in this white paper.

CHALLENGE

The adaptive capacity of organisms that may be impacted bychanging ocean chemistry is not well known, and a greatdeal of work must be done to understand the interactions ofmultiple stressors and their potential ramifications for marineecosystems and the human communities that depend on theirhealth. Further, while OA due to an increased atmospheric CO2concentration occurs in all marine waters, carbonate chemistryin coastal waters is affected by additional processes, such asnutrient addition and its effect on respiration, meaning thatcoastal acidification may be driven by more factors than just theincrease in atmospheric CO2.

The longest time-series observing assets to date have beendeployed within several open-ocean environments where theyhave documented surface water pCO2 values mostly trackingthe long-term trend in rising atmospheric CO2 (Figure 3),demonstrating that the global ocean carbon storage has increasedsince 2000 (Blunden et al., 2018; Feely et al., 2018; Le Quéréet al., 2018). Recent observations within shelf waters have beenshown in some regions to lag atmospheric CO2, indicating atendency for enhanced shelf uptake of atmospheric CO2 fromthe aqueous phase into biomass (Laruelle et al., 2018). Othercoastal regions exhibit more rapid increases in pCO2 relative tothe open ocean, indicating more rapid acidification due to theadditive effects of CO2 uptake and increased upwelling (Chavezet al., 2017). Coastal seas have been suggested to have changedin the recent past from a net source to a net sink (Bauer et al.,2013; Fennel et al., 2018; Laruelle et al., 2018). The enhanceduptake of CO2 by the ocean and shelves also changes the rateat which waters acidify, altering local rates of acidification, aprocess not well simulated by coarse global simulation modelsnor adequately captured by many direct measurements fromthe existing observing system. The local processes that governthese modifications may also serve to amplify (or dampen) global

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FIGURE 1 | Annual number of peer-reviewed publications on ocean acidification and number of authors involved during the period 1900–2018. Figure produced byJean-Pierre Gattuso using the bibliographic database of the IAEA Ocean Acidification International Coordination Centre (OA-ICC).

FIGURE 2 | Global distribution of ocean acidification publications by country, based on first author affiliation. Data from the IAEA Ocean Acidification InternationalCoordination Centre (OA-ICC).

changes expected from global earth system model projections,potentially altering the ecological consequences for shelf systems.

In addition to variability in time, the rates of uptake ofCO2 from the atmosphere also vary spatially, especially incoastal and shelf seas (Fennel et al., 2018; Laruelle et al.,2018). The magnitude of the sink of carbon has been shownto vary latitudinally, with high latitude (north of 30◦) coastalseas providing a sink while low latitude shelves are generallya source or neutral (Cai et al., 2006; Bauer et al., 2013; Chenet al., 2013). Spatial and temporal variability poses a challengeto the observational and modeling communities that couldbe better addressed with new tools and sensors, capabilitiesand technologies (see Next Generation Sensor Technologiesto Enhance the Observing System), and through internationalcollaborative efforts like GOA-ON. The scientific challenges that

the coastal variability imparts on stakeholders, managers, coastalcommunities, and other marine resource end-users poses uniquechallenges for attribution science, habitat shift projections, andstress response timing for vulnerable ecosystems. Below wedescribe some of the new tools, capabilities, and technologiesavailable to be ported through new informational products servedthrough GOA-ON, as well as the empowerment this globalnetwork offers coastal communities.

NETWORK GENESIS AND CONTEXT

Ocean observation, monitoring systems, and networks aredesigned to quantify variability and long-term changes, andto discover natural dynamics and anthropogenic impacts. The

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FIGURE 3 | Time series of in situ pCO2 (top) and pHT (bottom) for three time series stations in the Atlantic and Pacific Oceans. Data sources: BATS data:http://batsftp.bios.edu/BATS/bottle/; Hot data: University of Hawaii (http://hahana.soest.hawaii.edu/hot/products/HOT_surface_CO2; ESTOC data:https://www.nodc.noaa.gov/archive/arc0051/0100064/1.1/data/0-data/).

Global Ocean Observing System (GOOS), now consideredthe core, community-vetted ocean observing system forguidance, utilizes the Framework for Ocean Observing toimplement an integrated and sustained ocean observingsystem (Intergovernmental Oceanographic Commission (IOC)-UNESCO, 2012). This systems approach is designed to be flexibleand to adapt to evolving scientific, technological, and societalneeds, helping to deliver an ocean observing system tailored touser needs and the mitigation of societal impact. Within thisframework, OA is included as one phenomenon for inorganiccarbon in the Essential Ocean Variables (EOV) suite1.

The genesis of a global OA observing network with amultidisciplinary focus can be traced to an internationallyauthored OceanObs’09 community white paper, An InternationalObservational Network for Ocean Acidification (Feely et al.,2010). This paper recommended “an integrated internationalinterdisciplinary program of ship-based hydrography, time-seriesmoorings, floats and gliders with carbon system, pH and oxygensensors, and ecological surveys to determine the large-scalechanges in the properties of ocean water and the associatedbiological responses to OA.” Following panel discussions atOceanObs’09, the groundswell of scientists interested in thiseffort increased and broadened in discipline and expertise. In2012, a workshop was held in Seattle, WA, United States, todesign a global OA observing network that would delineate thephysical–chemical processes controlling the acidification of theoceans and their large-scale biological impacts and was alignedwith the EOV process. Workshop participants defined the goalsand requirements of a global OA observing network in thecontext of responding to societal needs.

Outcomes of the Seattle meeting were community definitionof the rationale, goals, design, suite of measurement parameters,

1GOOS EOV Suite: http://www.goosocean.org/components/com_oe/oe.php?task=download&id=35906&version=2.0&lang=1&format=1.

data quality objectives, data distribution strategies, andintegration with international programs (Newton et al.,2013). The rationale and design of the components and locationsconsidered existing networks and programs and identified gapsin both open-ocean and coastal regions. The minimum suite ofmeasurement parameters and performance metrics identifiedtwo different usage cases with the data quality objectives neededto support these: (1) “Climate” is defined as measurementsof quality sufficient to assess long-term trends with a definedlevel of confidence. With respect to OA, climate-quality datasupport detection of the long-term anthropogenically drivenchanges in hydrographic conditions and carbon chemistryover multidecadal timescales. (2) “Weather” is defined asmeasurements of quality sufficient to identify relative spatialpatterns and short-term variation, particularly in nearshoreregions where variability is higher (Table 1). Weather-qualitydata support mechanistic interpretation of the ecosystemresponse to OA and understanding of local, immediate OAdynamics. The name, Global Ocean Acidification ObservingNetwork (GOA-ON), was coined at the workshop2.

GOA-ON serves three goals to (1) improve understanding ofglobal OA conditions; (2) improve understanding of ecosystemresponse to OA; and (3) acquire and exchange data andknowledge necessary to optimize modeling of OA and itsimpacts (Newton et al., 2015). Thus, GOA-ON focuses on bothchemistry and biology, and through its data portal3, it providesdiscoverability of—and in some cases access to—data for myriaduses, including to improve forecast modeling and prediction ofthe future ocean.

The GOA-ON community held a second workshop in St.Andrews, United Kingdom, in 2013 to refine the vision for thestructure of GOA-ON, with emphasis on defining monitoring

2GOA-ON website: https://www.goa-on.org.3http://portal.goa-on.org/Explorer

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TABLE 1 | Recommended measurement uncertainties for climate and weatherfrom Newton et al. (2015).

Parameter Climate Uncertainty Weather Uncertainty

TCO2 2 µmol/kg 10 µmol/kg

TA 2 µmol/kg 10 µmol/kg

pCO2 2 µatm 10 µatm

pH 0.003 0.02

Aragonite Saturation 0.04 0.2

Calcite Saturation 0.06 0.3

for ecosystem impacts of OA in shelf and coastal seas (Newtonet al., 2013). After this workshop, the development of a dataportal commenced to provide OA-relevant asset locations andmetadata, with a vision toward serving data products. Theportal was made possible through an initial investment by theUniversity of Washington and by leveraging existing capacityfunded by the United States Integrated Ocean Observing System(U.S. IOOS). GOA-ON reached out to its members to populatethe data portal, housed at the GOA-ON website, with theirobserving information.

At a third workshop in Hobart, Australia, in 2016, majoroutcomes were related to the building and reinforcementof communities to increase regional coordination, withidentification of regional implementation needs, includinginformation, data products, and capacity building. The GOA-ONmentorship program known as “Pier2Peer” (described below)was launched at this workshop. Regional OA networks, actingas regional hubs of GOA-ON, have emerged in Latin America,Africa, the Western Pacific, Europe, the South Pacific Islands, andNorth America. Advances have been made in capacity building,and the GOA-ON community has expanded to more than600 members from 94 countries as of March 2019 (Figure 4).A fourth workshop in April 2019 in Hangzhou, China, targeted

further development of a coordinated network and regionalengagement. Workshop themes covered were ocean and coastalacidification in a multi-stressor environment; observing oceanand coastal acidification and impacts on ecosystems; modelingand forecasting ocean and coastal acidification and ecosystemresponses; and focusing GOA-ON efforts for societal benefit,stakeholder needs, and capacity building.

The vision for the future of the global OA observing network,described in this white paper, is built around eight components:(1) Optimize GOA-ON to better inform modeling communityneeds; (2) Fill gaps in understanding of chemical changes andbiological impacts; (3) Promote and advise the development ofnext generation sensor technology; (4) Support the growth ofregional hubs and grassroots establishment of new hubs; (5)Expand and enhance capacity-building efforts to enable broaderparticipation; (6) Improve the GOA-ON data portal; (7) Build OAnetworks producing scientific data and information designed toinform regional and international environmental action; and (8)Enhance collaboration with other observing networks.

GOA-ON REQUIREMENTS ANDGOVERNANCE

Ocean acidification is a global issue, but it has local effects thatdiffer depending on the environment (e.g., sensitivity of localspecies), and societal uses of the ocean and its resources. Anapproach that coordinates effort, so that global as well as localstatus could be assessed effectively and with consistent methods,was deemed necessary during the initial workshops held by GOA-ON. The OA data quality definition of Climate and Weather,based on data application, was an important step for GOA-ON.Many international or local climate assessments require climatequality data both in the open ocean and coastal seas (Karl et al.,2010). The inherent variability in coastal areas results in more

FIGURE 4 | Countries with GOA-ON members as of April 2019 are shaded black, excluding representatives of UN bodies.

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years of climate-quality data being required to observe trends(Sutton et al., 2018) compared to the open ocean. Uses such asmonitoring for aquaculture and biological experiments, or forinterpretations of local mechanisms underlying temporal andspatial variation can be served by either weather-quality data orclimate-quality data.

Three levels of measurements were defined for the twoobservational goals, with level 1 being critical measurements,level 2 enhanced measurements that allow further understanding,and level 3 those in development or experimental measurements.In general, it was much easier for the community to definerequirements for goal 1, OA status, than for goal 2, ecosystemresponse. For the latter, the participants considered diverseenvironments, such as polar, temperate, tropical, nearshore,and coral habitats.

Goal 1 level 1 variables are: temperature, salinity, oxygen,depth, and carbon-system constraints. Carbon-systemconstraints are achievable in a number of ways, includingcombinations of direct measurements and estimates based onmeasurements of at least two carbon-system variables. Twofurther variables, fluorescence and irradiance, were consideredimportant, except where the platform is not appropriate oravailable for such measurements. Goal 2 variables provideadditional detail, and the “level” requirements are defined byusage. In general, these include the goal 1 variables named above,plus variables describing phytoplankton, zooplankton, benthicproducers and consumers in shelf seas and nearshore, nutrients,organic carbon and nitrogen, and microbial measures.

The outcome from the GOA-ON vision and plan is to enableglobally accessible high-quality data and data synthesis productsthat facilitate research and new knowledge on OA, communicatethe status of OA and biological response, and enable forecastingof OA conditions. End-uses of these data include supportfor the development of national and international policy andadaptive action, including those related to carbon emissionpolicies, food security and livelihoods, fisheries and shellfishaquaculture practices, protection of coral reefs, shore protection,cultural identity, and tourism. However, investment in capacityin multiple areas critical to meet these needs must be addressed,including physical observing infrastructure, operations andmaintenance, data QA/QC, analytical and synthesis activities,and the intellectual infrastructure.

Since the launch of the Global Ocean Acidification ObservingNetwork in 2013, forward momentum has been maintained by anExecutive Council of experts from around the world who eitherrepresent core scientific disciplines or international or nationalinstitutions with a leadership role in the network. A distributedsecretariat was established in 2018 with support from theInternational Atomic Energy Agency, the IntergovernmentalOceanographic Commission, and the U.S. National Oceanicand Atmospheric Administration (NOAA) Ocean AcidificationProgram. The secretariat has a key role in the developmentof GOA-ON through the coordination and communication ofactivities and in building science-policy linkages. The data portaland website services are also part of the distributed secretariat,supported by NOAA’s Ocean Acidification Program, U.S. IOOS,and the University of Washington.

STATUS OF THE OBSERVING NETWORK

The observing network cataloged and guided by GOA-ONrepresents a multinational coordination effort to harmonizeocean observing strategies aimed toward acquiring robustevidence on OA and its worldwide impacts, guiding managementaction from regional to international levels, and informingpolicy decisions. Participating scientists adhere closely to theestablished observing requirements detailed in the GOA-ONRequirements and Governance document (Newton et al., 2015),which is oriented around the three goals outlined in Section“Network Genesis and Context” of this paper. In accordancewith these requirements, the existing observing networkis composed of assets deployed across multiple ecosystemdomains ranging from large-scale open-ocean regions to coastalenvironments inclusive of large estuaries and embayments. Assetsdeployed by GOA-ON participants are located in ecosystemsas divergent as the Arctic pelagic seas to tropical coral reefsand use of a broad range of asset types from ship-basedsampling to diver collection teams. Perhaps the most uniqueaspect of the GOA-ON observing network is the emphasison interdisciplinary observations including carbon chemistry,meteorology, oceanography, biogeochemistry, ecology, andbiology. The goal is not only to track OA, but also to understandand monitor the ecological changes that may result, and this setsGOA-ON apart from many other observing systems.

One example of this transdisciplinary approach is thestrategy employed in coral reef monitoring. NOAA established acoordinated national coral reef monitoring strategy that includesa broad suite of OA-relevant ecological metrics, including theadoption of standardized Calcium Carbonate Accretion (CCA)and bioerosion indices, which are deployed in tandem withregular carbonate chemistry monitoring (pCO2sea, pCO2air, andpH) together with temperature, salinity, oxygen, fluorescence,and turbidity. The protocols and methods adopted by NOAAfor coral reef OA monitoring have since been shared with theinternational community through a series of workshops that havefostered the adoption of similar methods throughout WesternPacific nations and elsewhere.

The current GOA-ON observing network4 is composed of 598assets deployed around the world and supported by 54 nations.The assets include 247 ship-based time series, 151 moorings,118 fixed ocean time series, 30 repeat hydrography lines, and22 volunteer observing ships (Figure 5). However, only abouttwo thirds of the reported assets include dual measures of thecarbonate system, which is a necessary minimum prerequisite forfully constraining the system as called for under the GOA-ONrequirements. Only about 30% of the assets on the portal haveassociated links to open-access data.

Many of the assets are deployed in specific open-oceanlocations and along coastal and shelf margins that are likely tobe heavily impacted by coastal biogeochemical processes. Thismakes direct detection of OA more challenging, particularlyin the absence of suitable regionally scaled biogeochemicalmodels that can be used for ascribing the specific drivers behind

4http://portal.goa-on.org/Explorer

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FIGURE 5 | Present-day (as of April 2019) Global Ocean Acidification Observing Network which is collaborative with the GO-SHIP, Ocean SITES, SOCONET, SOOPcommunities and other open-ocean and coastal observing networks.

the observed carbonate dynamics. Furthermore, many of theimpacted harvestable marine species reside below the mixed layerdepth while most of the observing system data to date are fromthe surface waters due to limited availability of sensors suitablefor deep-water deployment.

The observing design is working increasingly towardcollecting biological data from the field to determine if impactspredicted based on laboratory experiments are occurring inthe natural environment. This includes the use of standardizedCCA accretion plates in the field to determine if CCA ratechanges identified in experiments are occurring in coral reefs.Almost half of the assets currently listed on the GOA-ON portalare measuring at least one biological variable (chlorophyll,cyanobacteria/bacteria, zooplankton, and/or phytoplankton).New monitoring indices such as pteropod shell condition arealso being explored using repeated ship-surveys along the U.SWest Coast. The identification of additional biological variablesand integration into the network through cooperation withexisting biological observing programs is discussed in thefollowing section.

A VISION FOR THE OCEANACIDIFICATION OBSERVING NETWORK

The observing network should be optimally configured to meetmodeling community needs and be fit to purpose. As detailedin the GOA-ON requirements (Newton et al., 2015), the purposecan include detection of OA, whereby assets should be deployedwhere anticipated time of emergence (ToE) of an OA signal abovebackground natural variability occurs within a few decades interms of biogeochemical changes, and within perhaps severaldecades in the case of ecological monitoring (Sutton et al., 2018).This detection requires “climate-quality” data, which involves

a more stringent accuracy and precision than may be neededfor some applications (Table 1). Models can also assist withdetermining this metric as long as the primary processes drivingthe carbonate dynamics are suitably constrained. A well validatedor data-assimilated model can be used to extend observationsinto the past and future. Global-scale models have been used topredict the ToE of an OA signal against the background of otherenvironmental changes (e.g., Gruber, 2011; Carter et al., 2016,2017; Henson et al., 2017; McKinley et al., 2017). High-resolutioncoastal models that connect large-scale open-ocean conditionswith changes in coastal regions, including coastal upwelling andcoral reef systems, are beginning to emerge (e.g., Mongin et al.,2016; Siedlecki et al., 2016; Turi et al., 2016).

In locations where the purpose of an OA observing assetis to monitor current conditions, the less stringent “weather-quality” constraints (Table 1) may meet requirements. Theobserving asset in this case should include a suite of observationsthat can adequately characterize biogeochemical OA conditionsmost relevant to applications such as near-real-time support ofindustry products. Examples include observing systems deployedat shellfish hatcheries at a number of facilities in the U.S.Northwest and Northeast (Barton et al., 2015). This level of data isoften available in near-real-time, making it a vital part of forecastevaluation and a key locus of interaction with stakeholders incoastal communities.

Additionally, non-sustained deployments should beconsidered in cases where heuristic algorithm developmentor mechanistic determinations are the aim. Observing initiativesdesignated for the purpose of characterizing the primary modesof variability and characterizing it by means of algorithmdevelopment and constraint can prove very valuable in scalingdirect observations in both time and space. Examples mightinclude flux and rate measurements such as at the benthicinterface or investigating mechanisms of predictability to enable

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forecast system development, perhaps by exploring the ways inwhich large-scale climate variability is communicated to regionalwaters and watersheds.

Observing technologies are becoming more autonomous andhighly resolved in time and space, which allows observingnetworks to become better connected with the coasts and thuscommunities impacted by the changing ocean. The design andimplementation of networks require them to be adaptable, sothey are able to continue to evolve with emerging technologies asthey become available. Coastal communities will be increasinglyaffected by changing ocean conditions and forecasts and real-timedata access will enable them to develop strategies to respond. Theco-location of chemical and biological measurements is neededto assess in situ impacts and helps build the capacity to developindices, metrics, and risk assessment for coastal ecosystems(Boyd et al., 2015; Bednaršek et al., 2016). The same observinginfrastructure should also provide or coordinate with measuresof other stressors including temperature change, hypoxia, andpollution that can amplify or attenuate OA responses andinfluence the physiology, ecology, and the adaptive capacity ofmarine organisms (Hurd et al., 2018).

Next Generation Sensor Technologies toEnhance the Observing SystemThe GOA-ON goal of improving our understanding of globalOA conditions will be strongly supported by the developmentof new sensor technology. Specifically, new technology is neededto quantify (1) the range of natural variability in diverse marineecosystems (e.g., Figure 6) (Harris et al., 2013); (2) the organismalresponse to different biogeochemical conditions (Boyd et al.,2015); and (3) long-term trends in biogeochemical parameters.A wide range of in situ measurements are desired but thosefocused on stressors, i.e., temperature, pCO2, inorganic carbonand pH, oxygen, nutrients, salinity (Breitburg et al., 2015),and biology (biomass, populations) (McQuillan and Robidart,2017) are high priorities, as discussed in Section “GOA-ONRequirements and Governance.” Accordingly, 10 years ago,OceanObs’09 papers (Borges et al., 2010; Byrne et al., 2010; Feelyet al., 2010) called for the development of autonomous sensorsand systems to quantify dissolved inorganic carbon (DIC) andtotal alkalinity (TA). There has been significant progress in thisdirection with successful in situ deployments of novel DIC andTA instruments (Spaulding et al., 2014; Fassbender et al., 2015;Wang et al., 2015). However, as stated in Byrne et al. (2010),“There are at least two principal impediments to widespreadutilization of in situ instrumentation: cost and complexity.” Thesechallenges remain and have limited the widespread use ofthe new devices.

Moreover, even for technologies that have been on the marketfor several years, data quality varies substantially based on theexperience level of the operators (McLaughlin et al., 2017).Continued opportunities for hands-on training, a task that isoften initiated by scientists themselves, will be necessary forhigh-quality data collection and widespread use of new andcomplex devices. Co-deployment with independent sensors isrecommended for new technologies (Bresnahan et al., 2014;

McLaughlin et al., 2017), further increasing the cost of obtaininghigh-quality data.

Sensor drift, or loss of accuracy over time, is also a persistentproblem. Even when accuracy requirements are relaxed, e.g., forweather quality data in a hatchery, confidence within a definedtolerance must be established. Ideally, sensor data should bevalidated with independent, in situ samples. Often, conventionalmethods based on bottle samples collected before and afterdeployment do not provide sufficient replicates to confidentlyconstrain sensor accuracy. Two highly advanced and widelyutilized sensors use innovative strategies to correct for drift.Optode-based O2 sensors, a technology that is considered to bemature, have been calibrated by exposing the sensors directly toair (Bittig and Körtzinger, 2015; Bushinsky et al., 2016). ISFET-based pH sensors use deep-water pH values as a pH standardfor drift correction (Johnson et al., 2017; Williams et al., 2017).Without these drift corrections for O2 and pH, the measurementswould not be able to quantify the small seasonal changes in openocean environments.

Simplified technology may be on the horizon. Promising newsensors for pH and pCO2 are being developed based on optodetime-resolved fluorescence technology similar to O2 optodes(Clarke et al., 2015, 2017). Inexpensive, low-power infraredCO2 sensors are now being used for oceanographic applications(Bastviken et al., 2015; Hunt et al., 2017). A miniatureelectrochemical sensor for combined measurements of pH andTA has recently been demonstrated (Briggs et al., 2017).

Deployment platforms are more sophisticated and able toaccommodate a wider array of sensor technologies (Riser et al.,2018). Profilers include free drifting subsurface floats (Mignotet al., 2018), biogeochemical Argo profilers (Williams et al.,2017, 2018), ice-tethered (wire climbing) profilers (Toole et al.,2011), and moored profilers (e.g., winch operated; Palevskyand Nicholson, 2018). Autonomous underwater gliders andvehicles, self-propelled surface gliders such as Saildrone, andfree-floating surface drifters are also becoming more commonfor oceanographic research in regions not readily accessible byresearch ships (Lindstrom et al., 2017). Cabled networks withpower and high bandwidth data transmission might also becomemore common in the future. The adaptation of existing sensortechnology to more diverse platforms is likely to continue toadvance GOA-ON objectives. One additional area that is likelyto improve is in our handling of big data sets, both in terms ofquality control and the ability to provide real-time diagnostics(Duarte et al., 2018).

While it is likely that we will be able to more readilyquantify the inorganic carbon system in the coming decade,other important parameters remain out of reach. Dissolved andparticulate organic carbon are two critical pieces of the carboncycle that might be affected by OA (Egea et al., 2018). Opticalmeasurements (fluorescence, absorption) of colored dissolvedorganic matter are useful proxies (e.g., Jørgensen et al., 2011), buta direct measurement of dissolved organic carbon (DOC) that canbe applied to a wide range of marine environments is needed.

A major objective of GOA-ON is to quantify relationshipsbetween marine organisms and stressors. While most researchon biological impacts of ocean change is based on IPCC

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FIGURE 6 | (Top) Distribution of aragonite saturation data (open bars) calculated from in situ pH and pCO2 measurements collected over 5 years at the NewportHydrographic Line mooring (NH-10) off the Oregon coast (United States). The gray and red bars represent estimates from these data using pre-industrial and futureCO2 levels. (Bottom) The saturation states at the Oregon shelf break at 116 m depth. Adapted from Harris et al. (2013).

predictions, new sensor technology reveals existing spatio-temporal complexity of the marine environment that oftenexceeds the envelope of predicted change (Harris et al., 2013). Thevariability can influence species responses to baseline changes(Boyd et al., 2016). In addition, and particularly regardingmarine benthic organisms, seawater physics and chemistry maysignificantly vary across small microclimates within habitats.Deployment of arrays of multiple sensors may help characterizethese systems (e.g., Leary et al., 2017). Combining sensor datawith biology remains an important but very young area ofresearch, and often requires interdisciplinary collaborations oradvanced training. New in situ sensor technology might makethis more feasible. Future exciting opportunities exist to combinebiogeochemical and physical measurements with sophisticatedautonomous bio-analytical systems that can characterize andquantify microbial populations (e.g., automated flow cytometry,Hunter-Cevera et al., 2016; in situ genetic analysis, McQuillanand Robidart, 2017). These approaches can potentially overcomethe challenge of connecting species biomass or composition withenvironmental variables by continuously monitoring over a widerange of conditions (Marrec et al., 2018).

The discussion above poignantly reveals the challengeswe face in developing new biogeochemical and biologicalsensors. Repeated “technological revolutions” have made usbelieve that technology will continue to advance indefinitely.Sensor transduction mechanisms, e.g., optical or electrochemicaltransduction, are mature. Most oceanographic sensors haveutilized building blocks from other areas (e.g., fiber optics,integrated circuits) in a combinatorial evolution (Arthur, 2009) tomake oceanographic sensors. New building blocks from material

science, molecular biology, miniaturization, and fluidics are likely(e.g., Briggs et al., 2017) but will there be new transductionmechanisms that we do not know of today?

Filling Gaps in Understanding ofBiological ImpactsAddressing OA to minimize impacts requires the developmentof a mechanistic understanding of biological effects. In turn,understanding shifts in ocean biodiversity due to global changerequires inclusion of “ocean weather” such as daily andseasonal variability in ocean chemistry, including changes in thatvariability due to OA (Bates et al., 2018). GOA-ON’s secondgoal calls for a greater understanding of biological impacts andstrong coordination of this research. Reviewing the requirementsfor biological observations as outlined in Newton et al. (2015),and bridging present and future variability in the carbonatesystem with ecosystem changes are the objectives of the GOA-ON biology working group. This group works toward threemain tasks:

Task 1: Inform the Chemical Monitoring ProgramAbout the Biological NeedsMarine organisms are often living in highly fluctuatingenvironmental conditions and experience an even widervariability through migrations, changes of environment atdifferent life-history stages or manipulation of their niche.Through local adaptation, species and ecosystems are often ableto survive the wide range of variability while stress is inducedin conditions deviating from present environmental conditions(Vargas et al., 2017). We need to better capture all the aspects of

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this variability; for example, predicting organism sensitivity andidentifying relevant future scenarios important for determiningappropriate laboratory treatments require capturing the yearlypH regime experienced by an organism, including extremes, suchas the minimum value experienced.

Task 2: Evaluate the Needs and Requirements of aBiological Monitoring ProgramIdentifying which biological variables to track as indicatorsof OA impact is extremely challenging. Traditional biologicalmonitoring programs tend to focus on identifying, counting,or weighing particular taxa or communities (Bednaršek et al.,2014; Gattuso et al., 2015). As the identity of these organismsand the subsequent structure of communities differs greatly fromplace to place, it is difficult to identify key marine species orcommunity types that can be monitored everywhere. Instead, theGOA-ON biology working group is aiming to identify ecosystem-level indicators that are likely to be impacted by OA, such asbiogeochemical biomarkers of acidification and other stressors.

Task 3: Develop a Theoretical Framework LinkingChemical Changes to Biological ResponseForecasting biological impacts is one of the most pressing andimportant challenges in the field of OA. An understanding ofwhat is driving biological responses to OA is critical as inputto biological and ecological models that allow us to expandfrom existing monitoring initiatives to a more comprehensivebiological response understanding. Using existing literature anda theoretical framework such as the niche theory, the GOA-ONbiology working group is developing a probabilistic approachaimed at identifying the species, ecosystems, and sites that arethe most at risk.

COORDINATION AMONG OCEANOBSERVING NETWORKS

The existing large-scale oceanic carbon observatory networkof the Global Ocean Ship-based Hydrographic InvestigationsProgram (GO-SHIP) surveys, the Surface Ocean CO2 ObservingNetwork (SOCONET), the Ship of Opportunity Program(SOOP) volunteer observing ships, and the Ocean SustainedInterdisciplinary Time-series Environment observation System(OceanSITES) time-series stations in the Atlantic, Pacific, andIndian Oceans have provided a backbone of observations of thecarbonate chemistry needed to address the problem of OA. Theseactivities are linked through the International Ocean CarbonCoordination Project. Much of our present understanding ofthe long-term changes in the carbonate system is derived fromthese repeat surveys and time series measurements in the openocean (Feely et al., 2004; Sabine et al., 2004; Carter et al.,2017; Williams et al., 2017). Enhancing these activities andexpanding the global time-series network with new carbonand pH sensors, particularly in the Southern Hemisphere, isproviding important information on the changing conditionsin both open-ocean and coastal environments that have beenextensively under-sampled in the past. At present, many of

the existing moored carbon observatories only measure pCO2in surface waters, which is of itself insufficient to constrainthe carbon system adequately for effective monitoring andforecasting OA conditions and the concomitant biologicaleffects. Future efforts will require additional observationswith an enhanced suite of physical, chemical, and biologicalsensors in the ocean.

The GOA-ON has been designed to be fully integrated andcollaborative with other large-scale ocean carbon observingnetworks cited above by enhancing these networks withadditional measurement capabilities, including additionalsensors, data assimilation and distribution of resources via theGOA-ON data portal and linking them with coastal observingnetworks that also address OA. The resulting network design iscoordinated to link existing efforts with a common resources,infrastructure, data, and modeling capabilities (Figure 5).

GO-SHIP plans are being augmented to include full watercolumn and underway pH measurements on every cruise (Sloyanet al., in review). Plans for further expansion include the additionof biological and bio-optical measurements for estimatingprimary production, carbon export, and species changes. TheSOCONET and SOOP networks, including volunteer observingships and moorings, are also being expanded to include pH andother carbon system parameters where practical (Wanninkhofet al., in review), and many OceanSITES moorings have beenoutfitted with pH, pCO2, and other biogeochemical sensors. Dataintegration, validation, and dissemination will continue to beimplemented through the Surface Ocean CO2 Atlas (SOCAT),the GLobal Ocean Data Analysis Project (GLODAP), and GOA-ON data portals.

Biological observations addressing the impact of OA oughtto be framed within existing efforts, such as the MarineBiodiversity Observation Network (MBON). The Group onEarth Observations and MBON have worked together todefine Essential Biodiversity Variables and GOOS has developed‘Biology and Ecosystem’ Essential Ocean Variables (Miloslavichet al., 2018; Muller-Karger et al., 2018). Synergistic effort amongthe biological and OA communities by bringing experts togetherto discuss a common set of core variables to gain a moreconsistent and informed understanding of biological responsesto OA is encouraged. Equally important will be the jointresponsibilities of capacity building, mentoring, data deliveryand outreach activities similar to those implemented by GOA-ON and partners and described in Sections “Data AccessThrough the Global Data Portal” and “Capacity Building andRegional Coordination.”

Future plans for enhancement of the GOA-ON networkinclude new observational time-series sites, new technologies,particularly autonomous observing platforms such as Saildronesand Biogeochemical Argo floats in both open-ocean and coastallocations, and the development of new modeling tools and datasynthesis products for depicting global and regional trends inacidification and associated responses of marine food webs andecosystems. Integration with emerging observing networks likethe Global Ocean Oxygen Network will provide a global focuson understanding multiple stressor impacts and feedbacks. Bycombining observational capabilities wherever feasible we will

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be better positioned to provide integrated information on thecombined effects of acidification and deoxygenation to scientists,stakeholders and the interested public.

DATA ACCESS THROUGH THE GLOBALDATA PORTAL

The GOA-ON data portal provides an overview of where and howOA is measured and provides capability to access and visualizedata and synthesis products. The inventory of assets can besearched interactively by region, platform type and variables, andobservation-based products include contoured worldwide datasuch as pH, aragonite saturation, and total CO2 from GLODAPand annual and decadal CO2-weighted fugacity from SOCAT.Icons are used to display observing assets, many of which includelinks to data and metadata and some display real-time data.Observing assets include both stationary platforms such as fixedtime series, moorings, and mobile platforms such as repeathydrography, ship-based time series, and volunteer observingships. For a given carbonate chemistry-measuring asset, themetadata include information on which parameters are measuredand are linked to data providers, and other details.

Open and public access to data is a central tenet forincreasing OA knowledge. Many members of GOA-ON who haveprovided coordinates for OA data-relevant observing platformsalso provide access to the data from those platforms. A significantchallenge is to facilitate better access to data in regions thatoverlap with the Exclusive Economic Zone (EEZ) of nationsthat restrict data access, declaring the information too sensitiveto share. These EEZ regions may be sites of large variabilityand change, and they are potentially high risk for OA impactson ecosystems and populations. GOA-ON will be working tofacilitate data access in all regions.

Improving the Data PortalThere are several ways to add value to how the GOA-ON DataExplorer portal visualizes products from local to global scales. Forexample, the Data Explorer shows calculated aragonite saturationstate (�), a biologically relevant value, for a few of the near real-time moorings. NOAA Pacific Marine Environment Laboratoryhas provided interactive box plots of monthly averaged aragonitesaturation and pH, with pie charts showing the percent oftime the measurements are below a given threshold value.The interactive feature of these plots allows for the pH oraragonite threshold to be adjusted up or down by the user.Thus, quantitative information on habitat suitability for differentspecies with individual tolerances can be observed. This sameapproach can be expanded to other fixed assets with time seriesdata. Another example is to utilize models of OA conditionsthat are calibrated and verified by observing data, providingregional and local forecast model output that can identifyhabitat suitability patterns in space and time. User confidencein the model output will be increased by a feature such as a“comparator” to compare model output and mooring data. Sucha feature was developed by the U.S. IOOS’ Northwest Association

of Networked Ocean Observing Systems (NANOOS)5 on theirData Explorer, which can be adapted to the portal. These twosuggestions are within the current capability of the portal toserve, but dependent on output from scientists who maintainand develop models and moorings. However, support to maintainand develop the models, moorings, and analyses is requiredand often lacking.

New products that synthesize data are needed to provideinformation on status and trends, summary statistics, andgraphics that are suitable for managers, policymakers, and thepublic. International buy-in and creative development are coreneeds for the portal development. GOA-ON envisions its dataportal to be serving rather than archiving data, and to leverageand collaborate with the International Oceanographic Data andInformation Exchange (IODE), National Oceanographic DataCentres (NODCs), and international data holdings, applying themetadata and data formats developed for the UN SDG 14.3.1reporting process (discussed in more detail in Section “2030Agenda”) and other national and regional data centers. Thevisualization of 14.3.1 data provided by UN member states via theGOA-ON portal will be a direct service to scientists, policymakersand stakeholders.

During the next decade it will be necessary to develop toolsand mechanisms to illustrate current and projected impacts ofOA on marine life (GOA-ON Goal 2). Collaborative effortsbetween GOA-ON, GOOS, and subject-specific efforts suchas the Ocean Biogeographic Information System (OBIS) andIntergovernmental Oceanographic Commission (IOC) WorkingGroup ‘International Group for Marine Ecological Time Series’(IGMETS), can be used to collect related data and information.Interoperability so that synthesis products can pull in bothchemical and biological data is imperative. Producing such toolsand visualization products will take substantial effort but doing sois at the heart of what society and scientists need; a way to easilyview OA and ecosystem response.

CAPACITY BUILDING AND REGIONALCOORDINATION

Building capacity is essential to fill gaps in regions wherethere are few observations and research on OA, but where OAcould have major consequences for livelihoods. Training coursesfocusing on resource-limited countries have been organizedthrough collaboration among GOA-ON, the InternationalAtomic Energy Agency’s Ocean Acidification InternationalCoordination Centre (IAEA OA-ICC), the US-based non-profitThe Ocean Foundation, the Intergovernmental OceanographicCommission of UNESCO (IOC-UNESCO), and partners fromthe scientific community, local and regional stakeholders.Over 40 capacity building opportunities held since 2012 havetrained over 480 researchers from 69 countries (Figure 7).The opportunities have ranged from training courses toregional coordination workshops, to support for participationin international conferences. The training courses have varied

5www.nanoos.org; Data Explorer: http://nvs.nanoos.org/.

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FIGURE 7 | Location and number of participants from developing countries involved in OA training workshops from 2012 to 2018.

in focus (e.g., chemistry, biology, data management) and level(basic to more advanced) depending on regional needs and havebeen adjusted in response to feedback from participants fromearly courses. Additional resources have also been developed[e.g., databases6, ‘Best practices’ documents, online discussionfora (OAIE7), e-learning tools, etc.] to reach a wider audience andfor sustaining OA research after the courses.

The lack of availability of instrumentation has hampered theestablishment of sustained measurements for many countries andresearch organizations. In response, simplified methods and kitsof equipment to measure weather-quality pH and TA, knownas ‘GOA-ON in a Box’8 have been developed9, with The OceanFoundation providing kits to fifteen countries in Africa, thePacific Small Island Developing States and the Caribbean.

GOA-ON also launched the Pier2Peer mentorship programin 2016 to facilitate one-on-one collaborations through directtransfer of expertise and advice by matching experiencedresearchers with early career researchers. Pier2Peer includes 93mentees from 50 countries and 62 mentors from 15 countries.Although the program does not have dedicated funding, it hasbenefitted from a scholarship program organized by The OceanFoundation10, which has provided some funding for trainingvisits and the establishment of new monitoring programs.The mentoring process has helped develop close workingrelationships between early career researchers and experts from

6OA-ICC databases: https://www.iaea.org/services/oa-icc/science-and-collaboration/data-access-and-management.7The Ocean Acidification Information Exchange: https://www.oainfoexchange.org/.8https://www.oainfoexchange.org/teams/GOA-ON-Community9https://news-oceanacidification-icc.org/2016/10/21/iaea-int7019-task-force-meeting-on-the-development-and-standardization-of-methodology-12-14-october-monaco/10https://www.oceanfdn.org/projects/hosted-projects/ocean-acidification

many institutions, and the feedback on small grants applicationsassociated with the Pier2Peer program has been an effective wayto encourage better grant writing skills.

A Vision for Enhancing and ExpandingCapacity BuildingCapacity building, including training, mentorship, and providingaccess to equipment is a priority for the GOA-ON community inrecognition of the strong disparity among scientific capabilitiesacross the globe. Tracking how global capacity changes over timewill be critical, especially to know whether scientists in resourcechallenged countries are able to maintain monitoring over timewith their respective country’s support (Figure 8).

Future fundraising strategies will rely on an ongoingcommunications effort that showcases both the power of a globalnetwork and the uses for local data. The resources raised mightsupport both regional trainings, including data management, andnew scientific projects advanced through Pier2Peer proposals.

Beyond maintenance and improvement of fundraisingand institutional support, the strategy for capacity buildingoperations in the next decade will focus on enhancing thenetwork and the direct exchange of expertise and technology atnational, regional, and global levels. The facilitation of directinteraction with established scientific experts through workshopsand mentorships has been one of the most successful componentsof GOA-ON, and it is relatively low-cost. Encouragingcollaboration and exchange of knowledge between peers aswell as experts has also been highly successful and will continueto be a cornerstone of capacity building.

The establishment of regional centers of excellence for sampleanalyses and training are possibilities, including the developmentof more advanced training in data quality control to ensure high-quality data sets are made available through publicly accessibleplatforms and eLearning resources. Equally important is the

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FIGURE 8 | Results from a gap analysis survey of in-country researchers by the IAEA, TOF, IOC-UNESCO, NOAA and others in 2016 to assess the status of adeveloping country’s ability to monitor OA or track its effect on relevant marine resources.

identification of data-serving platforms (or proposals to createnew ones) so that every scientist, regardless of country, has anonline repository for serving of data.

Capacity building and training workshops have also identifieda number of technical challenges to address. The developmentof low-cost and simple-to-use equipment, such as handheldspectrophotometric pH analyzers, will be essential for theongoing success of this work. The sustainable production ofcertified reference materials covering a range of salinities fromestuaries to the open ocean and the provision of purified pHindicator dyes that are affordable and accessible are commonrequirements for the community.

The demand for training from developing countries and accessto appropriate technology is expected to increase in the nextdecade as many countries begin to report toward SDG 14.3.1,which is discussed in detail in Section “2030 Agenda.” GOA-ON’s role in coordinating and providing capacity building willbe increasingly important to make sure that limited resourcesare used in the best way possible. Periodic assessment throughsurveys of both the effectiveness and long-term sustainabilityof these efforts, which were initiated with regional and/orinternational funds, will rely on networks like GOA-ON.

The Importance and Future Role ofRegional HubsRegional networks or “hubs” are an essential component of GOA-ON’s operating structure because they allow for geographically-specific coordination and local expertise to address needs andgaps in OA monitoring. The hubs are formed in a grassrootsmanner and are self-governing with GOA-ON providing advice

and support and a representative of each hub serves onthe Executive Council. Seven hubs are currently providingopportunities for regional networking, collaboration, training,and the identification of region-specific priorities and scientificgaps: LAOCA11, the IOC-WESTPAC OA Program12, the OA-Africa Network13, and the North American Ocean AcidificationNetwork14, the Pacific Islands and Territories Ocean Acidificationnetwork (PI-TOA)15, Northeast Atlantic16, and Mediterraneanhubs17.

Two priority areas for future hubs are the Arctic and SouthernOceans. These are regions where biological impacts due to OAmay already be occurring (Kawaguchi et al., 2013; Bednaršeket al., 2016; Rastrick et al., 2018) and the skill of modelsin predicting changes are least certain (Lenton et al., 2013;Kwiatkowski and Orr, 2018).

Regional hubs will continue to be essential for meeting futureneeds for GOA-ON’s three goals. Local and regional collaborationis easier to maintain logistically, encourages collaboration amongscientists studying the same or adjacent ocean and coastalsystems, and coordinates localized knowledge of potentialsocioeconomic impacts. OA is progressing differently acrossvarious coastal areas and regions; therefore, it is important

11http://laoca.cl/en/12http://iocwestpac.org/oa/870.html13https://www.oa-africa.net/14http://goa-on.org/regional_hubs/north_america/about/introduction.php15http://goa-on.org/regional_hubs/pitoa/about/introduction.php16https://www.pml.ac.uk/Research/Projects/North_East_Atlantic_hub_of_the_Global_Ocean_Acidif17http://goa-on.org/regional_hubs/mediterranean/about/introduction.php

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to have geographically localized coordination that is largelyindependent of a more global approach.

The GOA-ON Executive Council will continue to ensurerepresentation of the hubs on the global stage and maintaina grassroots approach to the formation and governance ofeach hub. Beyond this, priorities for the regional hubs fromthe perspective of the GOA-ON Executive Council include: (1)continued support and capacity building where possible; (2)increased scientific collaboration within and between the hubs;(3) increased sharing of best practices among hubs and betweenthe GOA-ON Executive Council and the hubs; (4) enhancedcommunication between the hubs and the GOA-ON ExecutiveCouncil on capacity-building needs and opportunities; and (5)the bottom–up formation of more hubs to create global coverageon a regional scale.

The Latin American Ocean AcidificationNetwork (LAOCA): Status and Vision ofthe First HubLAOCA was the first regional hub formed by GOA-ON members.The LAOCA Network was officially established in December2015 during the 1st Latin American Workshop on Acidificationof the Oceans in Concepcion, Chile. Representatives fromArgentina, Brazil, Chile, Colombia, Ecuador, Mexico, and Perufounded the Network. At this first meeting, the members of theLAOCA network stressed the importance of biodiversity in LatinAmerican ecosystems and their willingness to cooperate and toshare the information. The first LAOCA Symposium for themembers was held in October 2017 in Buenos Aires, Argentina,with the addition of Costa Rica as a new member. This meetingwas a unique opportunity to share results about OA observationand research in the region and emphasized the potential ofongoing and future research to address common challenges.

The LAOCA research strategies include:

(i) The study of the carbonate system in coastal, oceanic, andestuarine waters, and its ecological and biogeochemicalimplications;

(ii) The experimental evaluation of the biological responsesof marine organisms to future scenarios of OA andinteraction with other climatic and anthropogenicstressors;

(iii) Modeling and projection of local and regional scenarios ofOA for Latin America based on monitoring at high spatialand temporal resolution; and

(iv) The effect on socio-ecological systems of theparticipating countries.

Over the past years, Latin American scientists have identifiedthe need to develop an observing strategy for monitoringfisheries, biodiversity, environmental variability and ecosystemmanagement at their coasts, considering the different levelsof observing capacity. Complementary experimental researchis needed to improve knowledge about ecosystem and speciesadaptation potential and the predictive capability of models.Additionally, LAOCA members have identified the need toquantify and improve our understanding of the changes and, in

particular, the consequences of OA on ocean and human health,to develop mitigation and adaptation strategies for society. Thechallenge is to improve communication with stakeholders andhelp make the best and boldest decisions. One key aspect isadvocating the issue of OA on the political agenda for thedifferent countries that take part in the LAOCA network.

At a regional symposium in Santa Marta, Colombia,in March 2018, several priorities were identified that areassociated with technical regional standardization, accessibilityto equipment and facilities, data and model availability, assertivecommunication at different levels, and policy relevance andrecognition. Common regional data storage and sharing facilitieshave also been identified as important to foster increasedcollaboration and harmonization of methods that will increasevisibility and best communicate the challenges and implicationsassociated with OA.

The vision for the next 10 years is to facilitate workingacross the region and expand participation to all countries withcoastal zones, convening scientists from different disciplines inorder to advance knowledge about OA, its quantification, and itsconsequences at local and regional levels. LAOCA will continuesharing knowledge through courses to train early-career scientistsfrom the Latin American and Caribbean regions entering theOA field. Finally, LAOCA needs to be a platform to engage withparticular stakeholder’s needs such as the aquaculture industry,artisanal fisheries or managers seeking environmental solutions.

BROADER INTERGOVERNMENTALCONSTRUCTS FOR OA ACTION

Like many other environmental problems, OA is a transboundaryproblem. While the top five countries for CO2 emissions areChina, the United States, India, Russia, and Japan (Janssens-Maenhout et al., 2017), model results show that the Arcticand Antarctic oceans, and the upwelling ocean waters off thewest coasts of North America, South America, and Africa areespecially vulnerable to OA (Jiang et al., 2015). In other words,the top emitters are not necessarily the countries experiencingthe worst effects from OA, which creates a disconnect betweenactions and impacts.

Many of the countries that will experience the worstimpacts of OA are those with limited scientific and technicalexpertise needed to establish monitoring efforts. Global observingnetworks such as GOA-ON are key mechanisms to supportcountries in building scientific capacity. They are also key toprovide international organizations, such as IOC-UNESCO, withtechnical advice to improve the political framework to enablescientific and observational knowledge generation needed tocombat the impacts of OA. GOA-ON has been explicitly notedin several intergovernmental fora as an exemplar of internationalscientific collaboration.

The assessment of international policy and governanceoptions addressing OA has highlighted the fragmented andinsufficient political preparedness for mitigating the effects of OAon marine ecosystems and ecosystem services (Herr et al., 2014).Since then, the 2030 Agenda, the UN Framework Convention on

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Climate Change (UNFCCC) with its Paris Agreement and therelated Marrakesh Global Climate Action Platform on Oceansand Coastal Areas, and the Global Climate Observing Systemhave provided the political rationale to foster and expand OAresearch and observation through networks like GOA-ON.

Additionally, past developments addressing adaptation toOA have emphasized the need to identify how OA will altermarine life and the ocean economy in the next decade. Thiswill allow the advancement of global and site-specific adaptationstrategies and increase the resilience of coastal communities (e.g.,Hennige et al., 2014; International Council for the Explorationof the Sea (ICES), 2014). The outcome is expected to feed backinto conventions and agreements, such as the Convention onBiological Diversity, the adaptation options within the UNFCCC,and regional fisheries bodies.

Fisheries and Aquaculture, Coral ReefProtection and Tourism, and OtherOA-Affected Societal Resources andTheir StakeholdersOcean acidification effects on many societally relevant issues,like fisheries, aquaculture, coral reef protection and tourism arelocally diverse, but need to be globally considered. For example, aglobally recognized but localized impact is the plight of PacificNorthwest U.S. shellfish growers who found their natural setsof oysters and their ability to grow shellfish larvae in hatcherieswas reduced in the early to mid-2000s (Barton et al., 2015). Thecombination of coastal upwelling of CO2-rich waters with theanthropogenic CO2 uptake tilted aragonite saturation states tolow values that impacted the oysters. For now, active monitoring,seawater buffering, and other adaptation practices have alleviatedthis issue for the hatcheries, but this example serves as a call toaction to connect the science to society, especially with respectto OA and fisheries and aquaculture. Globally, the multiplestressors of OA, rising temperatures, hypoxia, and harmful algalblooms will conspire to affect coastal fisheries and aquacultureindustries upon which many individuals, cultures, and nationsdepend. The new Food and Agriculture Organization of theUnited Nations synthesis volume on “Impacts of climate changeon fisheries and aquaculture” outlines impacts, vulnerabilities,and adaptations for marine fisheries in regional seas and focuseson the need for methods and tools for adaptation (Barangeet al., 2018). Close collaboration of GOA-ON with fisheries andaquaculture is a critical area for growth and focused attention inthe coming decade.

Coral reefs affect coastal economies and ecology indisproportionate ways. While coral reefs cover only 0.16%of the sea surface, they host about 30% of all known marinespecies and are essential to about 500 million people, generatingat least $300–400 billion per year in terms of food and livelihoodsfrom tourism, fisheries, coastal protection and medicines.A recent workshop organized by the Centre Scientifique deMonaco and the IAEA OA-ICC identified nine commonsolutions for six major coral reef regions and individual localizedsolutions for each of the diverse reef systems (Hilmi et al.,2018). These examples emphasize the need for a coordinated

OA observation network that is relevant to both local andglobal scales and one that is integrated nimbly across thesescales. Local lessons learned and the most efficacious observingstrategies to enable adaptation are best shared globally byintentional coordination.

2030 AgendaWithin the UN 2030 Agenda, the aim of SDG 14 is to “conserveand sustainably use the oceans, seas, and marine resources,” andconsists of 10 targets. GOA-ON supports countries to achieveTarget 14.3, which aims to “minimize and address the impactsof OA, including through scientific cooperation at all levels.”The progress made toward this target by all UN Member Statesis measured by the corresponding indicator 14.3.1 “Averagemarine acidity (pH) measured at agreed suite of representativesampling stations.” IOC-UNESCO is the custodian agencyfor this indicator and was tasked to develop an indicatormethodology (Intergovernmental Oceanographic Commission(IOC)-UNESCO, 2018)18. GOA-ON provided expert-level inputinto the methodology, which provides detailed guidance toscientists and countries in terms of what to measure, andhow to follow best practice guidelines established by the OAcommunity. It also includes recommendations on how to reportand openly share the collected information in a manner thatensures it is transparent, traceable, and useable for globalcomparison of pH measurements. Through this process, GOA-ON directly contributes to the achievement of SDG Target 14.3.The collective expertise of GOA-ON in science and policy ensuresthe development of a guiding vision for the collection andsharing of ocean chemistry data, which in the future is envisagedto extend to biological data. The development of the 14.3.1methodology is the first step in this process.

A streamlined reporting mechanism to obtain acomprehensive OA data set on an annual basis via connectingdata providers and different types of data repositories is a mainobjective of the SDG 14.3.1 methodology. IODE-associatedNODCs and Associated Data Units were surveyed in 2018 aboutthe biogeochemical data they hosted, including which of the fourcarbonate chemistry parameters (pH, TA, DIC, CO2) they served.More than 50% of these data centers were found to not serveany OA data, which might be due to no active OA observationin the region/country, limited capacity by the respectiveNODCs to hold this kind of information, or that scientistsare directly submitting relevant data to international and/orregional data centers, such as PANGAEA19 and the IntegratedCarbon Observation System20. A newly developed 14.3.1 OceanAcidification Data portal to be launched in 2019 to assist inachieving the full implementation of the 14.3.1 methodology andincreasing the capacity of countries to share data.

The 2030 Agenda framework provides many ways tosupport GOA-ON goal 1 (Figure 9). Voluntary Commitmentsare initiatives undertaken by Governments, the United Nations

18See IOC/EC-LI/2 Annex 6 http://unesdoc.unesco.org/images/0026/002651/265127e.pdf.19https://www.pangaea.de/20https://www.icos-ri.eu/

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FIGURE 9 | Scheme illustrating the pathways for input to the 2030 Agenda for ocean acidification observations.

system, other intergovernmental organizations, international andregional financial institutions, non-governmental organizationsand civil society organizations, academic and researchinstitutions, the scientific community, the private sector,philanthropic organizations and other actors—individually orin partnership—that aim to contribute to the implementationof SDG 14. There are currently 247 Voluntary Commitmentsthat address OA, and 61 are of direct relevance to it. TheVoluntary Commitments are organized in a Community ofOcean Action. GOA-ON submitted a Voluntary Commitment(#OceanAction16542)21, which includes support for measuringOA, storage, and data visualization by 2020. However, thesedeliverables will only be accomplished with continuous andincreasing financial commitment by countries and organizationsto establish and sustain OA observations. The UN OceanConference 2020 will be the time to assess achievements fromVoluntary Commitments and how to proceed.

UN Framework Convention on ClimateChangeOcean acidification gained further recognition through itsadoption as a Global Climate Indicator in 2018. The GlobalClimate Indicators are a suite of seven parameters, presented tothe UNFCCC, that describe the changing climate in an effort torecognize impacts beyond temperature change. The Indicatorsinclude atmospheric composition, energy, ocean, water and the

21https://oceanconference.un.org/commitments/?id=16542

cryosphere. The inclusion of OA in this list shows the importanceof guidance to achieve global alignment in observing OA asprovided in the SDG target indicator 14.3.1 methodology.

CONCLUSION

On a global scale, the building blocks of an integratedOA network in the open ocean are well established andquality-control mechanisms are in place (e.g., Climate andOcean: Variability, Predictability, and Change [CLIVAR]/GO-SHIP, OceanSITES, SOCONET, SOOP, SOCAT). However, earlyconsensus of the GOA-ON community is that there is asubstantial need for increased observation in many coastal areas,particularly in upwelling regions, regions strongly influencedby freshwater, and coral reef environments (Newton et al.,2015). Components of the open ocean system, including theSouthern Hemisphere oceans and the polar seas of the Arctic andAntarctic, are poorly sampled and need enhancement throughthe application of new technology and optimal use of ships andother observing platforms in the region.

For shelf seas and coasts, a global network for assessmentof OA is under construction as a high priority for GOA-ON.At the regional level, there are some systems in place withability to leverage OA observations on existing infrastructure(e.g., World Association of Marine Stations, InternationalLong-Term Ecological Research Network), although many gapsremain. These elements need a globally consistent design,

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which must also be coordinated and implemented on aregional scale. The Regional Hubs of GOA-ON provide thepeople-to-people foundation for enhancement of these coastalobservations, ensuring that data collected can answer regionallyrelevant questions.

In the coming decade, the GOA-ON will be a criticalresource for meeting the SDG 14.3 target, to “minimize andaddress the impacts of OA, including through enhanced scientificcooperation at all levels” through expert advice and by facilitatingthe provision of data to support the associated indicator. Buildingthe capacity of countries to submit data to this indicator willbe a guiding priority for the GOA-ON Executive Council in thecoming years. By facilitating the collection of data in support ofSDG 14.3, GOA-ON contributes to the sustainable use of theocean envisioned by the 2030 Agenda. In addition, a focus ondeveloping better, more reliable, easy to use, and hopefully lower-cost technologies for data collection of existing and newly vettedparameters, both autonomously and handheld, will supportthese SDG efforts.

The UN has proclaimed a Decade of Ocean Science forSustainable Development (2021–2030) to support efforts toreverse the cycle of decline in ocean health and gather oceanstakeholders worldwide behind a common framework, whichwill ensure ocean science can fully support countries in creatingimproved conditions for sustainable development of the Ocean.Ocean Science—research and observation—focusing on theimpact of multiple stressors on the marine ecosystems, includingOA, will be at the heart of the Decade. GOA-ON’s activitieswill be important stepping stones to develop the mitigationand adaptation strategies for sustainable management of oceanresources. Improving the current knowledge on how OA affectsocean economy is essential to predict the consequences of change,design mitigation, and guide adaptation.

Significant progress has been made in the past decade to fosteran integrated, leveraged approach to tracking and understandingOA through direct observation. The GOA-ON, a cornerstone ofthis broader effort, will work to move the community forward torealize this collective vision.

Recommendations• Coordination among scientists from a range of disciplines

(from chemistry to biology to technology development)and from across the globe including developing regions,particularly by:

◦ co-locating chemical and biological measurements tobuild capacity to develop indices, metrics, and riskassessments;

◦ articulating needed biological metrics to chemicalmonitoring programs;

◦ collaboratively evaluating the needs and requirementsof a global biological monitoring program; and

◦ developing a theoretical framework linking chemicalchanges to biological responses.

• Government, private, and United Nations support for OAobserving efforts;

• Develop and enhance regional cohorts working together onregionally specific OA issues;

• Make observational data from the open ocean to coastal toestuarine systems publicly accessible as much as possible;

• Develop capacity so that countries have expertise andguidance needed to report OA data as part of theSustainable Development Goal 14.3.1 process;

• Promote even closer integration between the Global OAObserving Network and other ocean observing networksfocusing on related measurements or issues toward thisshared vision;

• Produce observation-based informational products usefulfor decision making, such as developing tools andmechanisms to visualize the impacts of OA on marine life;

• Optimize the observing system to better support modelingcommunity needs, especially for coastal systems;

• New networks should consider prioritizing the followingwhen considering the future of their OA observingnetworks:

◦ to support monitoring that can contribute to Timeof Emergence calculations, some data sets acquiredshould be from the same location, similar timewindow, and of “climate quality”;

◦ to support forecasting and model development, someobservations should be prioritized to be real-time ornear-real-time;

◦ targeted observing initiatives designated for thepurpose of characterizing the primary modes ofvariability that include subsurface observations;

◦ co-located physical, chemical, and biologicalobservations to assist in co-stressor andattribution research.

• Encourage research to fill gaps in understanding of thebiological, ecological, and socioeconomic impacts of OA,particularly by enhanced research on the impacts andinteractions of multiple stressors on marine ecosystems;

• Promote the development of next generation sensortechnology, particularly new technology that enhancesability to quantify:

◦ the range of natural variability in diverse marineecosystems; and

◦ the organismal response to different biogeochemicalconditions;

◦ long-term trends in biogeochemical parameters.

• Expand and enhance capacity building efforts to enablebroader participation in OA observing and researchthrough:

◦ continued growth and support of scientificmentorship activities;

◦ further development of regional centers of excellencewhich can host ongoing trainings and analyze watersamples;

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◦ provision of advanced trainings that include lessonson data quality control and quality assurance;

◦ identification and development of accessible,sustainable data hosting platforms; and

◦ periodic assessment of global, regional, and localcapacity to conduct OA research.

AUTHOR CONTRIBUTIONS

BT, EJ, MD, JH-A, RF, DKG, LH, KI, MK, JN, SS, and FCcontributed to the conception and design of the manuscript andprovided text that served as the foundation for the manuscriptdevelopment. BT, EJ, RF, and JN led the review, the design, andthe development of the manuscript, with much assistance fromML, SD, DG, ML, MD, EC, and LK. CP, MG, KS, and MT gatheredand incorporated larger community input for the manuscript. Allauthors contributed to the manuscript revision and have read andapproved the submitted version.

FUNDING

The secretariat support provided by the IOC-UNESCO,the International Atomic Energy Agency, and the NOAAOcean Acidification Program (OAP) is central to the GOA-ON effort. GOA-ON also acknowledges NOAA OAP, theUniversity of Washington, U.S. IOOS, and NANOOS for supportof the GOA-ON data portal and website, and The OceanFoundation and government agencies for capacity buildingand training support. The Climate Science Centre of CSIROOceans and Atmosphere and the Integrated Marine ObservingSystem funded the contribution of BT. EJ, RF, DKG, MK,and DG were funded by the NOAA Ocean Acidification

Program. MD participation was funded by the U.S. NationalScience Foundation. JN thanks the University of Washington’sApplied Physics Laboratory and College of the Environment,NOAA OAP, U.S. IOOS, and NANOOS, and the WashingtonOcean Acidifdication Center for support for her role in thiscontribution. MT acknowledges support from the U.S. NationalScience Foundation grant OCE-1840868 to the ScientificCommittee on Oceanic Research (SCOR, U.S.). KI and KSthank the Government of Germany for its financial supportto the ocean acidification activities at the IntergovernmentalOceanographic Commission of UNESCO (IOC-UNESCO). LHcontributions were funded by the International Atomic EnergyAgency Ocean Acidification International Coordination Centre(OA-ICC), supported by several Member States via the IAEAPeaceful Uses Initiative. MK contributions were funded by theUnited States Department of State through an IAEA JuniorProfessional Officer position. The IAEA is grateful for the supportprovided to its Environment Laboratories by the Government ofthe Principality of Monaco.

ACKNOWLEDGMENTS

This community white paper was the collective work of manyresearchers. Over 600 members of GOA-ON, and especially thepast and present members of the executive committee, have beencritical to the development of an ongoing collaborative networkto address ocean acidification and the goals outlined in this paper.The authors thank the two reviewers and the editor FM-K, fortheir insightful comments, which have improved the manuscript.The authors also thank Sandra Bigley (NOAA PMEL) for herediting assistance that greatly contributed to this manuscript.This is Contribution Number 4877 from the NOAA PacificMarine Environmental Laboratory.

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Conflict of Interest Statement: The authors declare that the research wasconducted in the absence of any commercial or financial relationships that couldbe construed as a potential conflict of interest.

The reviewer PB declared a past co-authorship with one of the authors LK to thehandling Editor.

Copyright © 2019 Tilbrook, Jewett, DeGrandpre, Hernandez-Ayon, Feely, Gledhill,Hansson, Isensee, Kurz, Newton, Siedlecki, Chai, Dupont, Graco, Calvo, Greeley,Kapsenberg, Lebrec, Pelejero, Schoo and Telszewski. This is an open-access articledistributed under the terms of the Creative Commons Attribution License (CC BY).The use, distribution or reproduction in other forums is permitted, provided theoriginal author(s) and the copyright owner(s) are credited and that the originalpublication in this journal is cited, in accordance with accepted academic practice. Nouse, distribution or reproduction is permitted which does not comply with these terms.

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